1. Field of the Invention
The present invention relates to a recirculating valve returns surplus fuel supplied to an engine of, for example, an automobile, etc, to a fuel supplying passage that communicates a fuel tank and the engine.
2. Description of the Related Art
A recirculating valve of an automobile fuel system according to the related art, is shown in FIG. 5. Generally, more than a required quantity of fuel is supplied from a fuel tank 3 to an engine 2 through a fuel supplying passage 5, and the surplus fuel is returned to the fuel tank 3 from a return passage 6. A recirculating valve 1 is provided between the engine 2 and the fuel tank 3, as shown in FIG. 5.
The recirculating valve 1 comprises the fuel supplying passage 5, which communicates the fuel tank 3 and a fuel filter 4. Fuel from the fuel tank 3 is sent through the recirculating valve 1 to the engine 2 through the fuel filter 4 as shown by arrow (1). The return passage 6 for returning the surplus fuel from the engine 2 return to the fuel tank 3. A communication passage 7 is provided between the fuel supplying passage 5 and the return passage 6. An annular space 8 is formed at a confluence portion of the return passage 6 and the communication passage 7.
In the annular space 8, a return side nozzle 8a and a communication passage side nozzle 8b are provided so as to be opposed to each other. A bimetallic disk 10 is arranged between the return side nozzle 8a and the communication passage side nozzle 8b and is held in place by a plurality of holding pieces 9 provided along its circumference. The bimetallic disk 10 has a curved shape and curves upward as shown in the figure when the temperature of the fuel is below a prescribed temperature, to close the return side nozzle 8a and at the same time open the communication passage side nozzle 8b. However, when the fuel temperature exceeds the prescribed temperature, the bimetallic disk 10 curves downward, in the opposite direction, and opens the return side nozzle 8a and at the same time closes the communication passage side nozzle 8b. 
When the fuel temperature is below the prescribed temperature, surplus fuel from the engine 2 enters the annular space 8 from the direction shown by arrow (2) and flows through the communication passage side nozzle 8b and the communication passage 7 in the direction of arrows (3) and (4) to the fuel supplying passage 5. Mixing the surplus fuel with fuel to be sent to the engine 2 helps to raise the temperature of the fuel. Therefore, a warm-up operation of the engine 2 is excellently performed.
When the warm-up operation of the engine 2 is completed and the engine 2 is warmed-up, the temperature of the surplus fuel returned to the fuel tank 3 is increased. When the temperature exceeds the prescribed temperature, the bimetallic disk 10 of the annular space 8 curves downward. Thus, opening the return side nozzle 8a and at simultaneously closing the communication passage side nozzle 8b. Therefore, as shown by arrows (5) and (6), the surplus fuel is returned to the fuel tank 3 through the return side nozzle 8a and the return passage 6. As a result, heated fuel is not sent to the engine 2, and therefore an excessive temperature increase of the engine 2 can be prevented (see German patent No. 3427396).
Thus, in the recirculating valve according to the related art, when the temperature of the fuel exceeds the prescribed temperature, all of the surplus fuel is returned to the fuel tank through the return passage 6. Therefore, immediately after changeover operation of the valve, the fuel from the fuel tank 3 is supplied directly to the engine 2 through the fuel filter 4, without being heated by mixing with the surplus fuel.
Meanwhile, in regards to the diesel oil used as the fuel of the engine 2, it is known that when the outside temperature is below approximately −5° C., wax in the diesel oil may solidify. Therefore, when the above-described conventional recirculating valve 1 is used in a cold location where the outside temperature is below approximately −5° C., a problem as will be described hereafter arises. When the temperature of the fuel exceeds the prescribed temperature, all of the surplus fuel is returned to the fuel tank 3 through the return passage 6. However, for a brief period after changeover operation of the valve, any wax that may have solidified in fuel that had been maintained at a temperature of below approximately −5° C., also flows to the fuel filter 4 through the fuel supplying passage 5. In this case, the wax adheres to the surface of the fuel filter 4, which may clog the fuel filter 4.